WMOD00298

• Title: Quantifying Ice Nucleation by Silver Iodide Aerosols
• Date: 5/1/1990
• State: CO
• Weather Modification - Doc Type: Report

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this study fractions active were determined with the aid of the

condensation nucleus counter, considered to give an estimate of total

<Aitken) particles. This is discussed further in the following section.

3.3 Aerosol Generation

Cloud condensation and ice nuclei for experimentation are

generated outside the dynamic cloud chamber and can be injected at any

point prior to or during an expansion. A small fan is used to induce

mixing. Po1ydisperse or nearly monodisperse CCN particles of various

compositions can be generated from aqueous solution using a bubbler

system. These solution droplets are dried in a diffusion type drier

before input directly into the chamber or into a Thermo Systems

Incorporated (TSI) Electrostatic Classifier (Model 307l). Particle
concentrations in the DCC prior to injection are typically controlled

to be < 0.1 cm-3. The activity of the CCN aerosols used are relatively

well behaved and can be predicted theoretically (Fitzgerald, 1975). CCN

concentration can be adjusted over the range 10 to 104 cm-3. Total

condensation nucleus concentration was not monitored in every

experiment; rather, equivalent timed injections were used for this

study, based on measurements of bubbler output usinga TSI Condensation

Nucleus Counter (Model 3020).
Ice nucleating aerosols were generated in a repeatable manner by

solution combustion within a large vertical dilution tunnel. Samples of

ice nuclei were taken directly from the tunnel just before injection

time and were stored in flexibe, electrically conductive bags

(Velostat). When po1ydisperse aerosols were to be injected, this

required dilution with -30oC dewpoint air, due to the high